Method for lcos dbr multilayer stack protection via sacrificial hardmask for rie and cmp processes

ABSTRACT

Processing methods may be performed to forming a pixel material in a semiconductor structure. The methods may include forming a sacrificial hardmask overlying an uppermost layer of an optical stack of the semiconductor structure, the uppermost layer having a thickness. The methods may include forming a via through the sacrificial hardmask in the optical stack by a first etch process unselective to a metal layer of the semiconductor structure. The methods may include filling the via with a fill material, wherein a portion of the fill material extends over the sacrificial hardmask and contacts the metal layer. The methods may include removing a portion of the fill material external to the via by a removal process selective to the fill material. The methods may also include removing the sacrificial hardmask by a second etch process selective to the sacrificial hardmask while maintaining the thickness of the uppermost layer.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present technology is related to the following applications, allconcurrently filed Nov. 20, 2020, and titled: “STRUCTURE AND METHOD OFADVANCED LCOS BACK-PLANE HAVING HIGHLY REFLECTIVE PIXEL VIAMETALLIZATION” (Attorney docket number: 44018467US01 (1198535)),“STRUCTURE AND METHOD OF MIRROR GROUNDING IN LCOS DEVICES” (Attorneydocket number: 44018465US01 (1198060)), “STRUCTURE AND METHOD OFBI-LAYER PIXEL ISOLATION IN ADVANCED LCOS BACK-PLANE” (Attorney docketnumber: 44018227US01 (1198053)), and “STRUCTURE AND METHOD OF ADVANCEDLCOS BACK-PLANE HAVING ROBUST PIXEL VIA METALLIZATION” (Attorney docketnumber: 44018466US01 (1198064)). The present technology is also relatedto “METHOD OF CMP INTEGRATION FOR IMPROVED OPTICAL UNIFORMITY INADVANCED LCOS BACK-PLANE” (Attorney docket number: 44018468US01(1198069)), filed ______. Each of these applications is herebyincorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

The present technology relates to semiconductor systems, processes, andequipment. More specifically, the present technology relates toprocesses and systems for forming and etching material layers on asemiconductor substrate.

BACKGROUND

Advanced liquid crystal on silicon (LCoS) devices are made possible byprocesses which produce intricately patterned material layers onsubstrate surfaces. Producing patterned material on a substrate requirescontrolled methods for removal of exposed material. Chemical etching isused for a variety of purposes including transferring a pattern inphotoresist into underlying layers, thinning layers, or thinning lateraldimensions of features already present on the surface. Often it isdesirable to have an etch process that etches one material faster thananother facilitating, for example, a pattern transfer process orindividual material removal. Such an etch process is said to beselective to the first material. As a result of the diversity ofmaterials, circuits, and processes, etch processes have been developedwith a selectivity towards a variety of materials.

Multilayer LCoS structures, such as those incorporating distributedBragg reflectors (DBRs), may incorporate layers of dielectric orconducting material formed in a series of fabrication operations. Insome cases, electrical contacts may be formed as high aspect ratiostructures connecting two or more conducting layers separated bydielectric material, such as a pixel material formed through the layersmaking up the DBR. The electrical contacts may be formed by filling avia in the DBR with a fill material. Subsequent removal processes may beemployed to remove excess fill material from a reflective surface of theDBR that may be unselective to the upper layer of the DBR. Due to thelack of selectivity to the DBR materials, removal processes may lackendpoint controls, and may thin a constituent layer of the DBR in anonuniform and uncontrolled way. Nonuniform or poorly controlledthinning of DBR layers may negatively impact the overall opticalperformance of the LCoS structure.

Thus, there is a need for improved systems and methods that can be usedto produce high quality devices and structures. These and other needsare addressed by the present technology.

SUMMARY

Processing methods may be performed to forming a pixel material in asemiconductor structure. The methods may include forming a sacrificialhardmask overlying an uppermost layer of an optical stack of thesemiconductor structure, the uppermost layer having a thickness. Themethods may include forming a via through the sacrificial hardmask inthe optical stack by a first etch process unselective to a metal layerof the semiconductor structure. The methods may include filling the viawith a fill material, wherein a portion of the fill material extendsover the sacrificial hardmask and contacts the metal layer. The methodsmay include removing a portion of the fill material external to the viaby a removal process selective to the fill material. The methods mayalso include removing the sacrificial hardmask by a second etch processselective to the sacrificial hardmask while maintaining the thickness ofthe uppermost layer.

In some embodiments, the sacrificial hardmask may be or include aceramic material. The sacrificial hardmask may be or include siliconoxide. The fill material may be or include one or more of copper,aluminum, cobalt, tungsten, ruthenium, or tantalum nitride. The removalprocess may include chemical mechanical polishing. The second etchprocess may include a wet etch process. Removing the sacrificialhardmask may maintain the pixel material proud of an upper surface ofthe optical stack. The pixel material may extend beyond the uppersurface of the optical stack by a distance exceeding 10 nm. Thesemiconductor structure may include the metal layer, a spacer layeroverlying the metal layer, a mirror layer overlying the spacer layer,and the optical stack overlying the mirror layer.

The present technology also encompasses semiconductor structuresincluding a semiconductor substrate. The structures may include a metallayer overlying the semiconductor substrate. The structures may includea spacer layer overlying the metal layer. The structures may include amirror layer overlying the spacer layer. The structures may include anoptical stack overlying the mirror layer. The structures may include apixel material extending from the metal layer to a distance beyond anupper surface of the optical stack.

In some embodiments, the distance exceeds 10 nm. The structures mayinclude a barrier layer overlying the pixel material and the opticalstack. The barrier layer may be or include silicon carbon nitride. Thepixel material may be or include one or more of aluminum, copper, orcobalt. The pixel material may be or include a refractory material. Thepixel material may be or include one or more of tungsten, ruthenium, ortantalum nitride. The optical stack may be or include a DistributedBragg Reflector (DBR).

The present technology also encompasses semiconductor structuresincluding a semiconductor substrate. The structures may include a metallayer overlying the semiconductor substrate. The structures may includea spacer layer overlying the metal layer. The structures may include amirror layer overlying the spacer layer. The structures may include anoptical stack overlying the mirror layer. The structures may include apixel material extending from the metal layer to an upper surface of theoptical stack. The upper surface of the optical stack may becharacterized by a surface roughness less than or about 10 nm.

In some embodiments, the surface roughness of the upper surface may beless than or about 5 nm. The pixel material may extend from the metallayer to a distance beyond the upper surface of the optical stack. Thedistance may exceed 10 nm.

Such technology may provide numerous benefits over conventional systemsand techniques. For example, embodiments of the present technology mayexhibit improved uniformity and control of optical stack dimensionsduring and after fabrication of LCoS structures. Such improvements mayresult in concurrent improvements in reflectivity of the optical stackand resulting optical performance of devices incorporating the LCoSstructures.

These and other embodiments, along with many of their advantages andfeatures, are described in more detail in conjunction with the belowdescription and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic top plan view of an exemplary processing systemaccording to some embodiments of the present technology.

FIG. 2 shows a schematic cross-sectional view of an exemplary processingsystem according to some embodiments of the present technology.

FIG. 3 shows selected operations in a method of forming a pixel materialin a semiconductor structure according to some embodiments of thepresent technology.

FIGS. 4A-41 illustrate schematic cross-sectional views of substratematerials on which selected operations are being performed according tosome embodiments of the present technology.

Several of the figures are included as schematics. It is to beunderstood that the figures are for illustrative purposes, and are notto be considered of scale unless specifically stated to be of scale.Additionally, as schematics, the figures are provided to aidcomprehension and may not include all aspects or information compared torealistic representations, and may include exaggerated material forillustrative purposes.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a letter thatdistinguishes among the similar components. If only the first referencelabel is used in the specification, the description is applicable to anyone of the similar components having the same first reference labelirrespective of the letter.

DETAILED DESCRIPTION

The present technology includes systems and components for semiconductorprocessing of liquid crystal on silicon (LCoS) back-plane devices.Semiconductor structures built with an embedded optical stack, such as adistributed Bragg reflector (DBR), can have dramatically enhancedoptical performance for increased display brightness and lower powerconsumption relative to other reflective back-plane structures forliquid crystal displays. In an LCoS pixel structure, an optical stack,such as an embedded DBR, may be interposed between a metal layer and aliquid crystal layer, where the electrical potential for actuating theliquid crystal layer may be provided by the metal layer. For example, apixel material may be formed through the DBR to provide an electricalcontact between the metal layer and the liquid crystal layer, as when atransparent conducting film overlies the DBR. The pixel material may beor include a metal or electrically conductive material.

Incorporating the optical stack in the LCoS back-plane can addcomplexity to fabrication processes, as when incorporating layers ofdielectric or conducting material formed in a series of fabricationoperations. In some cases, forming the pixel material may includeforming a via in the optical stack and filling the via with a fillmaterial to subsequently form the pixel material. Processes for fillingthe via may include forming an overlying layer of the fill material, forexample, when a common substrate includes multiple pixel structuresmaking up a display system. Subsequent operations involving removing aportion of the fill material to reveal the reflective upper surface ofthe optical stack may have limited selectivity with respect to thematerial making up the upper surface optical stack. For example,chemical mechanical polishing (CMP) may remove a portion of an uppermostlayer of the optical stack, which in turn may negatively impact theoptical performance of the optical stack. The reflectivity of a DBR, forexample, may depend to a significant degree on the thicknesses of theconstituent layers making up the DBR. For this reason, deviation fromas-deposited layer thicknesses may reduce the reflectivity of the DBRand the overall optical performance of the LCoS device. Endpoint controlof CMP may not be available for typical high-k materials from which theupper layer of a DBR can be constructed. For at least this reason,operations for forming the pixel material may introduce uniformityissues in LCoS back-plane structures, and may negatively impact theoptical performance of optical stacks.

The present technology overcomes such limitations through an improvedpixel material structure and fabrication method, as described below. Insome embodiments, the methods include forming a pixel material toconnect an underlying metal layer and an overlying transparentconductive layer. A sacrificial hardmask may be formed overlying theoptical stack prior to forming a via, where the sacrificial hardmask canbe or include a material selected for low selectivity under CMP and highselectivity under etch processes. In this way, CMP for removal of excessfill material may end on the sacrificial hardmask, rather than an uppersurface of the optical stack. For a DBR, for example, maintaining thethickness of the uppermost layer preserves the optical properties of theDBR. In this way, including a sacrificial hardmask, which can beselectively removed following CMP, can protect the DBR and improve theoptical performance of the LCoS structure. In some embodiments, removingthe sacrificial hardmask may provide a pixel material proud of the uppersurface of the optical stack by a distance equivalent to the thicknessof the sacrificial hardmask, which may increase contact area of thepixel material and an overlying conductive layer.

Although the remaining disclosure will routinely identify specificetching processes utilizing the disclosed technology, it will be readilyunderstood that the systems and methods are equally applicable todeposition and cleaning processes as may occur in the describedchambers. Accordingly, the technology should not be considered to be solimited as for use with etching processes alone. The disclosure willdiscuss one possible system and chamber that can be used with thepresent technology to perform certain of the removal operations beforedescribing operations of an exemplary process sequence according to thepresent technology.

FIG. 1 shows a top plan view of one embodiment of a processing system 10of deposition, etching, baking, and/or curing chambers according toembodiments. The tool or processing system 10 depicted in FIG. 1 maycontain a plurality of process chambers, 24 a-d, a transfer chamber 20,a service chamber 26, an integrated metrology chamber 28, and a pair ofload lock chambers 16 a-b. The process chambers may include any numberof structures or components, as well as any number or combination ofprocessing chambers.

To transport substrates among the chambers, the transfer chamber 20 maycontain a robotic transport mechanism 22. The transport mechanism 22 mayhave a pair of substrate transport blades 22 a attached to the distalends of extendible arms 22 b, respectively. The blades 22 a may be usedfor carrying individual substrates to and from the process chambers. Inoperation, one of the substrate transport blades such as blade 22 a ofthe transport mechanism 22 may retrieve a substrate W from one of theload lock chambers such as chambers 16 a-b and carry substrate W to afirst stage of processing, for example, a treatment process as describedbelow in chambers 24 a-d. The chambers may be included to performindividual or combined operations of the described technology. Forexample, while one or more chambers may be configured to perform adeposition or etching operation, one or more other chambers may beconfigured to perform a pre-treatment operation and/or one or morepost-treatment operations described. Any number of configurations areencompassed by the present technology, which may also perform any numberof additional fabrication operations typically performed insemiconductor processing.

If the chamber is occupied, the robot may wait until the processing iscomplete and then remove the processed substrate from the chamber withone blade 22 a and may insert a new substrate with a second blade. Oncethe substrate is processed, it may then be moved to a second stage ofprocessing. For each move, the transport mechanism 22 generally may haveone blade carrying a substrate and one blade empty to execute asubstrate exchange. The transport mechanism 22 may wait at each chamberuntil an exchange can be accomplished.

Once processing is complete within the process chambers, the transportmechanism 22 may move the substrate W from the last process chamber andtransport the substrate W to a cassette within the load lock chambers 16a-b. From the load lock chambers 16 a-b, the substrate may move into afactory interface 12. The factory interface 12 generally may operate totransfer substrates between pod loaders 14 a-d in an atmosphericpressure clean environment and the load lock chambers 16 a-b. The cleanenvironment in factory interface 12 may be generally provided throughair filtration processes, such as HEPA filtration, for example. Factoryinterface 12 may also include a substrate orienter/aligner that may beused to properly align the substrates prior to processing. At least onesubstrate robot, such as robots 18 a-b, may be positioned in factoryinterface 12 to transport substrates between various positions/locationswithin factory interface 12 and to other locations in communicationtherewith. Robots 18 a-b may be configured to travel along a tracksystem within factory interface 12 from a first end to a second end ofthe factory interface 12.

The processing system 10 may further include an integrated metrologychamber 28 to provide control signals, which may provide adaptivecontrol over any of the processes being performed in the processingchambers. The integrated metrology chamber 28 may include any of avariety of metrological devices to measure various film properties, suchas thickness, roughness, composition, and the metrology devices mayfurther be capable of characterizing grating parameters such as criticaldimensions, sidewall angle, and feature height under vacuum in anautomated manner.

Each of processing chambers 24 a-d may be configured to perform one ormore process steps in the fabrication of a semiconductor structure, andany number of processing chambers and combinations of processingchambers may be used on multi-chamber processing system 10.

For example, any of the processing chambers may be configured to performa number of substrate processing operations including any number ofdeposition processes including cyclical layer deposition, atomic layerdeposition, chemical vapor deposition, physical vapor deposition, aswell as other operations including etch, pre-clean, pre-treatment,post-treatment, anneal, plasma processing, degas, orientation, and othersubstrate processes. Some specific processes that may be performed inany of the chambers or in any combination of chambers may be metaldeposition, surface cleaning and preparation, thermal annealing such asrapid thermal processing, and plasma processing. Any other processes maysimilarly be performed in specific chambers incorporated intomulti-chamber processing system 10, including any process describedbelow, as would be readily appreciated by the skilled artisan.

FIG. 2 illustrates a schematic cross-sectional view of an exemplaryprocessing chamber 100 suitable for patterning a material layer disposedon a substrate 302 in the processing chamber 100. The exemplaryprocessing chamber 100 is suitable for performing a patterning process,although it is to be understood that aspects of the present technologymay be performed in any number of chambers, and substrate supportsaccording to the present technology may be included in etching chambers,deposition chambers, treatment chambers, or any other processingchamber. The plasma processing chamber 100 may include a chamber body105 defining a chamber volume 101 in which a substrate may be processed.The chamber body 105 may have sidewalls 112 and a bottom 118 which arecoupled with ground 126. The sidewalls 112 may have a liner 115 toprotect the sidewalls 112 and extend the time between maintenance cyclesof the plasma processing chamber 100. The dimensions of the chamber body105 and related components of the plasma processing chamber 100 are notlimited and generally may be proportionally larger than the size of thesubstrate 302 to be processed therein. Examples of substrate sizesinclude 200 mm diameter, 250 mm diameter, 300 mm diameter and 450 mmdiameter, among others, such as display or solar cell substrates aswell.

The chamber body 105 may support a chamber lid assembly 110 to enclosethe chamber volume 101. The chamber body 105 may be fabricated fromaluminum or other suitable materials. A substrate access port 113 may beformed through the sidewall 112 of the chamber body 105, facilitatingthe transfer of the substrate 302 into and out of the plasma processingchamber 100. The access port 113 may be coupled with a transfer chamberand/or other chambers of a substrate processing system as previouslydescribed. A pumping port 145 may be formed through the sidewall 112 ofthe chamber body 105 and connected to the chamber volume 101. A pumpingdevice may be coupled through the pumping port 145 to the chamber volume101 to evacuate and control the pressure within the processing volume.The pumping device may include one or more pumps and throttle valves.

A gas panel 160 may be coupled by a gas line 167 with the chamber body105 to supply process gases into the chamber volume 101. The gas panel160 may include one or more process gas sources 161, 162, 163, 164 andmay additionally include inert gases, non-reactive gases, and reactivegases, as may be utilized for any number of processes. Examples ofprocess gases that may be provided by the gas panel 160 include, but arenot limited to, hydrocarbon containing gas including methane, sulfurhexafluoride, silicon chloride, tetrafluoromethane, hydrogen bromide,hydrocarbon containing gas, argon gas, chlorine, nitrogen, helium, oroxygen gas, as well as any number of additional materials. Additionally,process gasses may include nitrogen, chlorine, fluorine, oxygen, andhydrogen containing gases such as BCl₃, C₂F₄, C₄F₈, C₄F₆, CHF₃, CH₂F₂,CH₃F, NF₃, NH₃, CO₂, SO₂, CO, N₂, NO₂, N₂O, and H₂ among any number ofadditional precursors.

Valves 166 may control the flow of the process gases from the sources161, 162, 163, 164 from the gas panel 160 and may be managed by acontroller 165. The flow of the gases supplied to the chamber body 105from the gas panel 160 may include combinations of the gases form one ormore sources. The lid assembly 110 may include a nozzle 114. The nozzle114 may be one or more ports for introducing the process gases from thesources 161, 162, 164, 163 of the gas panel 160 into the chamber volume101. After the process gases are introduced into the plasma processingchamber 100, the gases may be energized to form plasma. An antenna 148,such as one or more inductor coils, may be provided adjacent to theplasma processing chamber 100. An antenna power supply 142 may power theantenna 148 through a match circuit 141 to inductively couple energy,such as RF energy, to the process gas to maintain a plasma formed fromthe process gas in the chamber volume 101 of the plasma processingchamber 100. Alternatively, or in addition to the antenna power supply142, process electrodes below the substrate 302 and/or above thesubstrate 302 may be used to capacitively couple RF power to the processgases to maintain the plasma within the chamber volume 101. Theoperation of the power supply 142 may be controlled by a controller,such as controller 165, that also controls the operation of othercomponents in the plasma processing chamber 100.

A substrate support pedestal 135 may be disposed in the chamber volume101 to support the substrate 302 during processing. The substratesupport pedestal 135 may include an electrostatic chuck 122 for holdingthe substrate 302 during processing. The electrostatic chuck (“ESC”) 122may use the electrostatic attraction to hold the substrate 302 to thesubstrate support pedestal 135. The ESC 122 may be powered by an RFpower supply 125 integrated with a match circuit 124. The ESC 122 mayinclude an electrode 121 embedded within a dielectric body. Theelectrode 121 may be coupled with the RF power supply 125 and mayprovide a bias which attracts plasma ions, formed by the process gasesin the chamber volume 101, to the ESC 122 and substrate 302 seated onthe pedestal. The RF power supply 125 may cycle on and off, or pulse,during processing of the substrate 302. The ESC 122 may have an isolator128 for the purpose of making the sidewall of the ESC 122 lessattractive to the plasma to prolong the maintenance life cycle of theESC 122. Additionally, the substrate support pedestal 135 may have acathode liner 136 to protect the sidewalls of the substrate supportpedestal 135 from the plasma gases and to extend the time betweenmaintenance of the plasma processing chamber 100.

Electrode 121 may be coupled with a power source 150. The power source150 may provide a chucking voltage of about 200 volts to about 2000volts to the electrode 121. The power source 150 may also include asystem controller for controlling the operation of the electrode 121 bydirecting a DC current to the electrode 121 for chucking and de-chuckingthe substrate 302. The ESC 122 may include heaters disposed within thepedestal and connected to a power source for heating the substrate,while a cooling base 129 supporting the ESC 122 may include conduits forcirculating a heat transfer fluid to maintain a temperature of the ESC122 and substrate 302 disposed thereon. The ESC 122 may be configured toperform in the temperature range required by the thermal budget of thedevice being fabricated on the substrate 302. For example, the ESC 122may be configured to maintain the substrate 302 at a temperature ofabout −150° C. or lower to about 500° C. or higher depending on theprocess being performed.

The cooling base 129 may be provided to assist in controlling thetemperature of the substrate 302. To mitigate process drift and time,the temperature of the substrate 302 may be maintained substantiallyconstant by the cooling base 129 throughout the time the substrate 302is in the cleaning chamber. In some embodiments, the temperature of thesubstrate 302 may be maintained throughout subsequent cleaning processesat temperatures between about −150° C. and about 500° C., although anytemperatures may be utilized. A cover ring 130 may be disposed on theESC 122 and along the periphery of the substrate support pedestal 135.The cover ring 130 may be configured to confine etching gases to adesired portion of the exposed top surface of the substrate 302, whileshielding the top surface of the substrate support pedestal 135 from theplasma environment inside the plasma processing chamber 100. Lift pinsmay be selectively translated through the substrate support pedestal 135to lift the substrate 302 above the substrate support pedestal 135 tofacilitate access to the substrate 302 by a transfer robot or othersuitable transfer mechanism as previously described.

The controller 165 may be utilized to control the process sequence,regulating the gas flows from the gas panel 160 into the plasmaprocessing chamber 100, and other process parameters. Software routines,when executed by the CPU, transform the CPU into a specific purposecomputer such as a controller, which may control the plasma processingchamber 100 such that the processes are performed in accordance with thepresent disclosure. The software routines may also be stored and/orexecuted by a second controller that may be associated with the plasmaprocessing chamber 100.

FIG. 3 shows selected operations in a method 300 of forming a pixelmaterial in a semiconductor structure according to some embodiments ofthe present technology. Many operations of method 300 may be performed,for example, in the chamber 100 as previously described. Method 300 mayinclude one or more operations prior to the initiation of the method,including front end processing, deposition, etching, polishing,cleaning, or any other operations that may be performed prior to thedescribed operations. The method may include optional operations asdenoted in the figure, which may or may not be specifically associatedwith some embodiments of methods according to the present technology.For example, many of the operations are described in order to provide abroader scope of the structural formation, but are not critical to thetechnology, or may be performed by alternative methodology as will bediscussed further below. Method 300 describes operations shownschematically in FIGS. 4A-4I, the illustrations of which will bedescribed in conjunction with the operations of method 300. It is to beunderstood that FIG. 4 illustrates only partial schematic views, and asubstrate may contain any number of semiconductor sections havingaspects as illustrated in the figures, as well as alternative structuralaspects that may still benefit from aspects of the present technology.Method 300 may involve optional operations to develop the semiconductorstructures to a particular fabrication operation.

In the context of method 300, the semiconductor structure 400 may definean active pixel, where the active pixel is described in reference toFIG. 4A. At one or more points in the formation processes leading to thesemiconductor structure 400, the operations of method 300 may beimplemented to form a conductive contact between constituent layers ofthe semiconductor structure 400, as described in reference to FIGS.4B-4I. A resulting display device, formed by a process including theoperations of method 300, may incorporate a semiconductor structure 400having a robust metallized pixel, and may therefore exhibit reduceddegradation during one or more fabrication processes subsequent theoperations of method 300.

As illustrated in FIG. 4A, the semiconductor structure 400 may representa liquid crystal on silicon (LCoS) back-plane comprising one or moreconstituent structures forming an active pixel. As illustrated,structure 400 may include a substrate 401 made of or containing siliconor some other semiconductor substrate material, on which the one or morestructures of the LCoS back-plane may be formed. For example, structure400 may include a metal layer 403, formed, for example, from copper oranother metal compatible with semiconductor processing techniques.Structure 400 may further include a reflective and conductive mirrorlayer 407 that may be or include aluminum, copper, or another reflectivematerial suitable for providing a mirror surface. To electricallyinsulate the mirror layer 407 from the metal layer 403, a spacermaterial 405 may be formed overlying the metal layer 403 prior toforming the mirror layer 407. The structure may include an optical stackproviding a reflective backing structure. As illustrated, the opticalstack can be or include a distributed Bragg reflector 409 (DBR), whichmay be formed overlying the mirror layer 407. In some embodiments, theoptical stack may include other reflective layers or structures,including, but not limited to dielectric mirrors or otherhigh-reflection coatings, In some embodiments, the DBR 409 may includemultiple alternating layers of high-k and low-k dielectric materials.For example, low-k layers 411 may be or include a low-k dielectricmaterial, such as silicon oxide or organosilicate glass. By contrast,high-k layers 413 may be or include a high-k dielectric material, suchas tantalum oxide.

For further implementation in LCoS devices, the semiconductor structuremay include a pixel material 415. As illustrated, the pixel material 415may extend from an upper surface 417 of the DBR 409 and contact themetal layer 403, which may provide a conductive path between the metallayer 403 and the upper surface 417, through an aperture in the mirrorlayer 407 and the DBR 409. As described in more detail in reference tothe forthcoming figures, the pixel material 415 may be or include ametal or a refractory material selected for suitability with downstreamprocessing operations such as high-temperature deposition and reactiveion etching.

In some embodiments, the mirror layer 407 may be physically separatedfrom active electrical components of the structure 400 to prevent ashort-circuit from affecting multiple pixels, as when the mirror layer407 spans multiple pixels on the LCoS device. For example, in structure400, the mirror layer 407 may be electrically isolated from the metallayer 403 and the pixel material 415. By contrast, the pixel materialmay be in electrical contact with an overlying transparent conductivelayer 419 formed on regions of the upper surface 417. In someembodiments, the transparent conductive layer 419 may be or include atransparent conductive oxide, such as indium tin oxide (ITO) or aluminumdoped zinc oxide, or a transparent conductive coating incorporatingcarbon allotropes including, but not limited to, graphene, diamond likecarbon, or carbon nanotubes. The transparent conductive layer 419 mayprovide transparency over one or more wavelength ranges and a conductivecontact to energize and actuate a liquid crystal layer overlying thestructure 400.

Forming the transparent conductive layer 419 may include plasmadeposition techniques. For example, in the case of ITO, forming thetransparent conductive layer 419 may include, but is not limited to,plasma enhanced chemical vapor deposition, chemical vapor deposition,spray pyrolysis, reactive e-beam evaporation, sputtering, or physicalvapor deposition. Deposition of the transparent conductive layer 419 maybe conducted in an oxidative environment, at elevated temperatures, orboth. In some embodiments, forming the transparent conductive layer 419may include baking operations, for example, in cases of conductive filmsformed by spin-coating. During the course of such operations, the pixelmaterial 415 may be exposed to reactive environments, oxidizingenvironments, or elevated temperatures, which may induce degradation andmay negatively impact the electrical contact formed between the metallayer 403 and the transparent conductive layer 419.

In some embodiments, pixels may be defined by pixel isolation structures421 formed on the upper surface 417, such that an individual pixel mayinclude a pixel material 415 and a transparent conductive layer 419,between two pixel isolation structures 421. In some embodiments, theLCoS backplane may include multiple pixels having the same structure400, from which a display system may be formed having an array ofaddressable pixels. The pixel isolation structures 421 may be or includea high-k material, such as the high-k material 413. In some embodiments,deposition of the pixel isolation structures 421 may be conducted atelevated temperatures at which the material of the pixel material 415may diffuse into the DBR 409 or the pixel isolation structures 421. Forexample, when the pixel material 415 is formed of a non-refractorymaterial selected for high reflectance or electrical conductivity, thepixel material 415 may be susceptible to degradation during formation ofthe pixel isolation structures 421.

As illustrated in an inset of FIG. 4A, the structure 400 may include apixel material 415 proud of the upper surface 417 of the DBR 409, where“proud” refers to one structure extending beyond another structure, inopposition to “flush,” where both structures are substantially coplanar.In some embodiments, the pixel material 415 may extend beyond the uppersurface 417 of the DBR 409 by a distance 423. As described in moredetail in reference to FIGS. 4B-4H, below, the distance 423 may resultfrom the removal of a sacrificial hardmask material formed as part ofthe method 300 that is removed prior to formation of the transparentconductive layer 419 or the pixel isolation structures 421. As such, thedistance 423 may correspond to one or more design constraints arisingout of the formation of the sacrificial hardmask. For example, thesacrificial hardmask may be formed at a thickness greater than a minimumthickness for effective protection of the upper surface 417 of the DBR409. In some embodiments, the distance 423 may be greater than or about10 nm, greater than or about 20 nm, greater than or about 30 nm, greaterthan or about 40 nm, greater than or about 50 nm, or larger.

Providing a pixel material 415 proud of the upper surface 417 of the DBRby the distance 423 may increase the surface contact area between thepixel material 415 and the overlying transparent conductive layer 419without substantially increasing the lateral cross section of the pixelmaterial. In some embodiments, the increased surface contact area mayimprove the quality of the electrical contact between the two structuresrelative to a pixel material 415 substantially level with the uppersurface 417 of the DBR 409. For example, electrical contact area betweenthe transparent conductive layer 419 and the pixel material 415 mayinfluence temporal dynamics of the LCoS device, as when implementinghigh-frequency switching. For example, larger contact area may reducecharge accumulation at the surface of the pixel material 415, which mayimprove peak voltage during operation.

At operation 305, a sacrificial hardmask 427 may be formed on an uppersurface 417 of the DBR 409, as illustrated in FIGS. 4B-4C. The structure400 may include a window 425 in the mirror layer 407. The operation 305may include depositing the sacrificial hardmask 427 overlying theoptical stack in the region of the window 425. The sacrificial hardmask427 can be or include a material selected to shield the upper surface417 of the DBR 409 from subsequent removal processes. For example, thesacrificial hardmask 427 may be or include a material resistant to CMP.Where the upper surface 417 of the DBR 409 may be susceptible to removalby CMP, the pixel material 415 may exhibit a selectivity relative to thesacrificial hardmask 427 of greater than or about 5:1, greater than orabout 10:1, greater than or about 20:1, greater than or about 40:1,greater than or about 50:1, greater than or about 100:1, or greater thanor about 200:1 to CMP employed in subsequent operations of the method300. In some embodiments, the sacrificial hardmask 427 can be or includesilicon, oxygen, nitrogen, metals, silicon oxide, polysiloxane, siliconcarbide, metal oxide, or other organo-siloxane or spin-on hardmaskmaterials.

The sacrificial hardmask 427 may be formed by methods compatible withmaterial deposition processes of the chamber 100. For example, thesacrificial hardmask 427 may be formed by CVD, ALD, or spin-onprocesses, dependent on the material selected. Spin-on processestypically describe techniques used to coat a wafer surface with a liquidhardmask precursor material. The liquid precursor may be dispensed ontothe wafer surface in a predetermined amount, before or while the waferis rapidly rotated, in some cases up to 6000 rpm. During spinning, theliquid precursor may be uniformly distributed on the wafer surface byinertia. Subsequently, the liquid precursor may be solidified by heatingto form the sacrificial hardmask 427.

The thickness of the sacrificial hardmask 427 may be a product ofcoupled processing chamber constraints and material properties. Whiledeposition processes may be compatible with forming the sacrificialhardmask 417 at any arbitrary thickness, process chamber constraints maylimit the maximum thickness to within an allowable headroom forsubsequent removal processes. For example, a CMP process may impose amaximum thickness on the sacrificial hardmask 427, arising from amaximum allowable headroom between a substrate and a polishing surface.In this way, the thickness of the sacrificial hardmask 427 may belimited to a maximum of less than or about 60 nm, less than or about 50nm, less than or about 40 nm, less than or about 30 nm, less than orabout 20 nm, or smaller. Similarly, material properties of thesacrificial hardmask 427 may introduce a minimum thickness beneath whichthe sacrificial hardmask 427 may prove ineffective at protecting theunderlying DBR 409 from removal during subsequent operations of themethod 300. For example, while removal of overlying materials by CMP maybe selective to the pixel material 415, an insufficient thickness of thesacrificial hardmask 427 may nonetheless result in the sacrificialhardmask 427 being removed and the

CMP removing a portion of the high-k material 413 of the DBR 409. Assuch, the minimum thickness of the sacrificial hardmask 427 may begreater than or about 5 nm, greater than or about 10 nm, greater than orabout 15 nm, greater than or about 20 nm, greater than or about 25 nm,greater than or about 30 nm, or larger, within the constraints imposedby the processing chamber employed to implement the method 300.

Subsequent forming the sacrificial hardmask 427, a via 429 may be formedat operation 310, as illustrated in FIG. 4D. The via 429 may be formedby a dry etch process to selectively remove portions of the sacrificialhardmask 427, the DBR 409, the mirror layer 407, and the spacer material405, to reveal the metal layer 403. In some embodiments, forming the via429 may include additional processes including, but not limited to,depositing a patterned etch mask including a window through which theetch process of operation 310 may form the via 429. For example, theetch mask may be or include a material resistant to oxide etching.Subsequent formation of the via 429, the etch mask may be removed bychemical etch techniques selective to the etch mask. In someembodiments, The via 429 may taper toward the metal layer 403. The tapermay facilitate subsequent high aspect ratio fill operations and mayfacilitate forming an electrical connection between the pixel material415 and the metal layer 403 in subsequent operations of the method 300.As illustrated in FIG. 4D, at the mirror layer 407, the via 429 may belaterally narrower than the width of the window 425, such that the via429 may form one or more sloped sidewalls extending from the surface ofthe DBR 417 to the metal layer 403, without intersecting the mirrorlayer 407.

Subsequent forming the via 429, the via 429 may be filled at operation315, as illustrated in FIG. 4E. Operation 315 may include filling thevia 429 by depositing a fill material 431 in the via 429 by one or moreprocesses including, but not limited to, chemical vapor deposition,atomic layer deposition, physical vapor deposition, or other techniquescompatible with semiconductor fabrication. The fill material 431 may bedeposited by a wafer-scale process and, as such, may include a portionoverlying the sacrificial hardmask 427. In some embodiments, the fillmaterial 431 from which the pixel material 415 is formed may be orinclude a material selected for stability under semiconductorfabrication processes including, but not limited to, thermal deposition,plasma-deposition, oxygen etch, or those producing other reactiveenvironments that may induce oxidation, thermal diffusion or otherdegradation in non-refractory metals. In some embodiments, the fillmaterial 431 can be or include tungsten, ruthenium, or tantalum nitride.As described in reference to FIG. 4A, the pixel material 415 may beformed prior to deposition of overlying layers or structures including,but not limited to, the transparent conductive layer 419 or the pixelisolation structures 421. The overlying layers or structures may beformed under elevated temperatures or in reactive or oxidizingenvironments, where a non-refractory material may be susceptible todegradation. As such, the fill material 431 may incorporate a refractorymaterial, such as those selected to resist oxidation, or thoseexhibiting a reduced diffusivity at process temperatures relative tonon-refractory materials such as copper or cobalt.

The fill material 431 may form an electrical contact with the metallayer 403. In some embodiments, non-refractory materials, such ascopper, cobalt, or aluminum, may present beneficial properties forinclusion as materials from which to construct the pixel material 415.For example, non-refractory materials may exhibit relatively highreflectance and electrical conductivity, which may facilitate theelectrical connection between the metal layer 403 to the transparentconductive layer 419 without significantly impacting the opticalperformance of the overall structure 400.

Subsequent filling the via 429, a portion of the fill material 431 maybe removed at operation 320, as illustrated in FIG. 4F. In someembodiments, the removal may include CMP removal of a portion of thefill material 431 overlying the sacrificial hardmask 427, therebyforming the pixel material 415. The CMP process may form a substantiallylevel surface between an upper surface 433 of the pixel material 415 andan upper surface 435 of the sacrificial hardmask 427. As describedabove, CMP may be unselective to the material from which the sacrificialhardmask 427 is formed and selective to the fill material 431. In thisway, the CMP process may uniformly remove the fill material 431 untilreaching the upper surface 435 of the sacrificial hardmask 427, at whichpoint the removal rate of the CMP process may decrease significantly,and thus may serve as an endpoint for the removal process. As such, theCMP process may selectively remove the portion of the fill material 431overlying the sacrificial hardmask 427, leaving the upper surface 417 ofthe DBR 409, and thus the optical properties of the DBR 409,substantially unaffected.

Subsequent removing the portion of the fill material, the sacrificialhardmask 427 may be removed at operation 325, as illustrated in FIGS.4G-H. The sacrificial hardmask 427, while resistant to CMP, may besusceptible to selective removal by chemical etch processes targeted atoxide materials. In this way, operation 325 may reveal the upper surface417 of the DBR 409, and may maintain the pixel material 415 proud of theupper surface 417 of the DBR 409. In some embodiments, operation 325 mayemploy removal techniques may including, but not limited to, wet acidetching or reactive ion etching, ion milling, or e-beam techniques toselectively remove the sacrificial hardmask 427. As a result ofselectively removing the sacrificial hardmask 427 while maintaining thepixel material 415, the upper surface 433 of the pixel material 415 mayextend from the upper surface 417 of the DBR 409 by the distance 423, asdescribed above in reference to FIG. 4A.

As illustrated in FIG. 4H, the upper surface 417 of the DBR 409 may becharacterized by a surface roughness 437, measured in units of lengthsuch as nanometers. Protecting the upper surface 417 from thinning byCMP, through deposition of the sacrificial hardmask 427, may produce ahigher surface roughness 437 of the upper surface 417 of the DBR 409relative to a surface polished by CMP. While the surface roughness 437may affect reflectivity of the structure 400, the thickness of thehigh-k layer 413 may have a more significant effect. Therefore, thestructure 400 may exhibit improved optical performance relative tostructures formed without the sacrificial hardmask 427. In someembodiments, the surface roughness 437 of the upper surface 417 of theDBR 409 may correspond to an as-deposited roughness resulting from thedeposition method employed during formation of the DBR 409. The surfaceroughness 437 may be less than or about 20 nm, less than or about 18 nm,less than or about 16 nm, less than or about 14 nm, less than or about12 nm, less than or about 10 nm, less than or about 8 nm, less than orabout 6 nm, less than or about 4 nm, less than or about 2 nm, less thanor about 1 nm, or less. The surface roughness 437 of the upper surface417 may have a significant impact on the reflection of light that isincident at glancing angles. A glancing angle may describe a non-normalangle. For example, roughness of the DBR layers may result in as much asa 3-5% reduction in reflection efficiency. In this way, reducing surfaceroughness, for example, below or about 2 nm, may improve the opticalperformance on a system level.

In some embodiments, the method 300 may include additional optionaloperations. For example, the method 300 may include operation 330, asillustrated in FIG. 41. In some embodiments, operation 330 may includeforming a barrier layer 437 overlying the pixel material 415 and theupper surface 417 of the DBR 409. The barrier layer 437 may be orinclude one or more materials selected to protect the pixel material 415from thermal and oxidative effects of the fabrication processes usedduring formation of the transparent conductive layer 419 and the pixelisolation structures 421. For example, the barrier layer 437 may be orinclude carbon or nitrogen containing compounds including, but notlimited to, silicon carbide, silicon nitride, or silicon carbon nitride.

In some embodiments, the barrier layer 437 may be or include nitrides oftitanium or tantalum, for example, when the pixel material 415 includesmetals such as copper, cobalt, or aluminum. In semiconductor processingoperations, such materials can be thermally stable and may not reactwith the pixel material 415. Other potential diffusion barrier materialsfor the semiconductor structure may be or include other binary nitridesincluding, but not limited to tantalum carbide, tungsten carbon nitride,tantalum carbon nitride, oxides of one or more of the preceding metals,silicon nitride, silicon carbon nitride, or ruthenium. In some cases,the aforementioned materials may exhibit barrier properties at layerthicknesses less than 15 nm, less than 5 nm, less than 3 nm, or smaller,depending on one or more properties of the semiconductor operations. Thebarrier layer 437 may be sacrificial, in that it may be removed prior toformation of the transparent conductive layer 419 and the pixelisolation structures 421. In this way, the structure 400 may include thepixel material 415 with negligible degradation resulting from theformation of the overlying structures.

In the preceding description, for the purposes of explanation, numerousdetails have been set forth in order to provide an understanding ofvarious embodiments of the present technology. It will be apparent toone skilled in the art, however, that certain embodiments may bepracticed without some of these details, or with additional details.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theembodiments. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent technology. Accordingly, the above description should not betaken as limiting the scope of the technology.

Where a range of values is provided, it is understood that eachintervening value, to the smallest fraction of the unit of the lowerlimit, unless the context clearly dictates otherwise, between the upperand lower limits of that range is also specifically disclosed. Anynarrower range between any stated values or unstated intervening valuesin a stated range and any other stated or intervening value in thatstated range is encompassed. The upper and lower limits of those smallerranges may independently be included or excluded in the range, and eachrange where either, neither, or both limits are included in the smallerranges is also encompassed within the technology, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “a layer” includes aplurality of such layers, and reference to “the precursor” includesreference to one or more precursors and equivalents thereof known tothose skilled in the art, and so forth.

Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”,“include(s)”, and “including”, when used in this specification and inthe following claims, are intended to specify the presence of statedfeatures, integers, components, or operations, but they do not precludethe presence or addition of one or more other features, integers,components, operations, acts, or groups.

What is claimed is:
 1. A method of forming a pixel material in asemiconductor structure, the method comprising: forming a sacrificialhardmask overlying an uppermost layer of an optical stack of thesemiconductor structure, the uppermost layer having a thickness; forminga via through the sacrificial hardmask in the optical stack by a firstetch process unselective to a metal layer of the semiconductorstructure; filling the via with a fill material, wherein a portion ofthe fill material extends over the sacrificial hardmask and contacts themetal layer; removing a portion of the fill material external to the viaby a removal process selective to the fill material; and removing thesacrificial hardmask by a second etch process selective to thesacrificial hardmask while maintaining the thickness of the uppermostlayer.
 2. The method of claim 1, wherein the sacrificial hardmaskcomprises a ceramic material.
 3. The method of claim 2, wherein thesacrificial hardmask comprises silicon oxide, and wherein the fillmaterial comprises one or more of copper, aluminum, cobalt, tungsten,ruthenium, or tantalum nitride.
 4. The method of claim 1, wherein theremoval process comprises chemical mechanical polishing and the secondetch process comprises a wet etch process.
 5. The method of claim 1,wherein removing the sacrificial hardmask maintains the pixel materialproud of an upper surface of the optical stack.
 6. The method of claim5, wherein the pixel material extends beyond the upper surface of theoptical stack by a distance exceeding 10 nm.
 7. The method of claim 1,wherein the semiconductor structure comprises: the metal layer; a spacerlayer overlying the metal layer; a mirror layer overlying the spacerlayer; and the optical stack overlying the mirror layer.
 8. Asemiconductor structure comprising: a semiconductor substrate; a metallayer overlying the semiconductor substrate; a spacer layer overlyingthe metal layer; a mirror layer overlying the spacer layer; an opticalstack overlying the mirror layer; and a pixel material extending fromthe metal layer to a distance beyond an upper surface of the opticalstack.
 9. The semiconductor structure of claim 8, wherein the distanceexceeds 10 nm.
 10. The semiconductor structure of claim 8, furthercomprising a barrier layer overlying the pixel material and the opticalstack, the barrier layer comprising silicon carbon nitride.
 11. Thesemiconductor structure of claim 10, wherein the pixel materialcomprises one or more of aluminum, copper, or cobalt.
 12. Thesemiconductor structure of claim 8, wherein the pixel material comprisesa refractory material.
 13. The semiconductor structure of claim 8,wherein the pixel material comprises one or more of tungsten, ruthenium,or tantalum nitride.
 14. The semiconductor structure of claim 8, whereinthe optical stack comprises a Distributed Bragg Reflector (DBR).
 15. Asemiconductor structure comprising: a semiconductor substrate; a metallayer overlying the semiconductor substrate; a spacer layer overlyingthe metal layer; a mirror layer overlying the spacer layer; an opticalstack overlying the mirror layer; and a pixel material extending fromthe metal layer to an upper surface of the optical stack, the uppersurface of the optical stack characterized by a surface roughness lessthan or about 10 nm.
 16. The semiconductor structure of claim 15,wherein the surface roughness of the upper surface is less than or about5 nm.
 17. The semiconductor structure of claim 15, wherein the pixelmaterial extends from the metal layer to a distance beyond the uppersurface of the optical stack.
 18. The semiconductor structure of claim17, wherein the distance exceeds 10 nm.
 19. The semiconductor structureof claim 15, wherein the pixel material comprises one or more of copper,cobalt, or aluminum.
 20. The semiconductor structure of claim 15,wherein the pixel material comprises one or more of tungsten, ruthenium,or tantalum nitride.